/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.adtech.adms.commons.web.filter;


import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;


/**
 * <p>Example filter that sets the character encoding to be used in parsing the
 * incoming request, either unconditionally or only if the client did not
 * specify a character encoding.  Configuration of this filter is based on
 * the following initialization parameters:</p>
 * <ul>
 * <li><strong>encoding</strong> - The character encoding to be configured
 *     for this request, either conditionally or unconditionally based on
 *     the <code>ignore</code> initialization parameter.  This parameter
 *     is required, so there is no default.</li>
 * <li><strong>ignore</strong> - If set to "true", any character encoding
 *     specified by the client is ignored, and the value returned by the
 *     <code>selectEncoding()</code> method is set.  If set to "false,
 *     <code>selectEncoding()</code> is called <strong>only</strong> if the
 *     client has not already specified an encoding.  By default, this
 *     parameter is set to "true".</li>
 * </ul>
 *
 * <p>Although this filter can be used unchanged, it is also easy to
 * subclass it and make the <code>selectEncoding()</code> method more
 * intelligent about what encoding to choose, based on characteristics of
 * the incoming request (such as the values of the <code>Accept-Language</code>
 * and <code>User-Agent</code> headers, or a value stashed in the current
 * user's session.</p>
 *
 * @author Craig McClanahan
 * @version $Revision: 1.1 $ $Date: 2010/03/11 05:48:28 $
 */

public class SetCharacterEncodingFilter implements Filter {


	// ----------------------------------------------------- Instance Variables


	/**
	 * The default character encoding to set for requests that pass through
	 * this filter.
	 */
	protected String encoding = null;


	/**
	 * The filter configuration object we are associated with.  If this value
	 * is null, this filter instance is not currently configured.
	 */
	protected FilterConfig filterConfig = null;


	/**
	 * Should a character encoding specified by the client be ignored?
	 */
	protected boolean ignore = true;


	// --------------------------------------------------------- Public Methods


	/**
	 * Take this filter out of service.
	 */
	public void destroy() {

		this.encoding = null;
		this.filterConfig = null;

	}


	/**
	 * Select and set (if specified) the character encoding to be used to
	 * interpret request parameters for this request.
	 *
	 * @param request The servlet request we are processing
	 * @param result The servlet response we are creating
	 * @param chain The filter chain we are processing
	 *
	 * @exception IOException if an input/output error occurs
	 * @exception ServletException if a servlet error occurs
	 */
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain)
	throws IOException, ServletException {

		// Conditionally select and set the character encoding to be used
		if (ignore || request.getCharacterEncoding() == null) {
			String encoding = selectEncoding(request);
			if (encoding != null) {
				request.setCharacterEncoding(encoding);
			}
		}

		// Pass control on to the next filter
		chain.doFilter(request, response);

	}


	/**
	 * Place this filter into service.
	 *
	 * @param filterConfig The filter configuration object
	 */
	public void init(FilterConfig filterConfig) throws ServletException {

		this.filterConfig = filterConfig;
		this.encoding = filterConfig.getInitParameter("encoding");
		String value = filterConfig.getInitParameter("ignore");
		if (value == null) {
			this.ignore = true;
		} else if (value.equalsIgnoreCase("true")) {
			this.ignore = true;
		} else if (value.equalsIgnoreCase("yes")) {
			this.ignore = true;
		} else {
			this.ignore = false;
		}

	}


	// ------------------------------------------------------ Protected Methods


	/**
	 * Select an appropriate character encoding to be used, based on the
	 * characteristics of the current request and/or filter initialization
	 * parameters.  If no character encoding should be set, return
	 * <code>null</code>.
	 * <p>
	 * The default implementation unconditionally returns the value configured
	 * by the <strong>encoding</strong> initialization parameter for this
	 * filter.
	 *
	 * @param request The servlet request we are processing
	 */
	protected String selectEncoding(ServletRequest request) {

		return this.encoding;

	}


}
